STAINING METHODS 35 



3. Dry the film. If the drop used is sufficiently small, the film 

 will dry readily at room temperature. The dryiag process may be 

 hastened by holding the cover glass in the fingers, high over the 

 flame. If the wet film is overheated, the preparation will be spoiled. 



4. Fix the bacteria to the cover glass by passing it three times 

 through the flame, holding the cover glass, film side up, in the 

 cover-glass forceps. This process coagulates the albuminous 

 substances and causes the bacteria to adhere firmly to the glass 

 through subsequent operations. 



5. Stain the preparation, keeping it still in the forceps. Place 

 on the film a few drops of the staining solution to be used. 

 Allow it to act five or ten minutes, the time depending some- 

 what on the species of bacteria and the stain employed. 



Instead of placing the stain upon the film, the cover glass 

 may be immersed in a small glass dish containing the stain. 

 Special cover-glass forceps are made for this purpose. If heat is 

 required to hasten or intensify the process, a watch glass holding 

 the stain is placed on the steam bath and in it the cover glass ; 

 or the cover glass with the stain upon it may be held over the 

 Bunsen flame, the stain being replenished as it is evaporated. 



6. Wash the cover glass in a weak stream of water. 



7. Put the wet cover glass, film side downward, on a slide. 

 Blot with filter paper and examine with the microscope. 



8. If it is desired to make a permanent preparation, the cover 

 glass should be dried in the air or gently over a flame, and then 

 mounted on a slide with Canada balsam. 



9. Label the slide, stating name of organism, stain employed, 

 date, and owner's name or initials. 



Exercise 60. Preparation of Contrast Stains 



1. Aqueous eosin. 



Eosin (water sollible) . . . . . 1 g. 



Distilled water 100 cc. 



Dissolve and add absolute alcohol .... 5 co. 



2. Bismarck brown (Vesuvin). 



Bismarck brown . 0.5 g. 



Distilled water 100.0 cc. 



